The invention relates to improvements in fluid flow machines in general, and more particularly to improvements in seals and fluid flow restrictors between the housings or casings and the flow guidance devices of such machines. Still more particularly, the invention relates to fluid leakage control systems in fluid flow machines, especially between the casings and diffusers of centrifugal pumps.
German Pat. No. 689618 granted Mar. 28, 1940 to Lindemann et al. discloses a system serving to compensate for different thermally induced expansion of neighboring machine parts which are not rotatable relative to each other and which are heated to different temperatures. Such compensation is often necessary in centrifugal pumps, especially in multi-stage centrifugal pumps which are used to convey hot fluids. Thermally induced expansion of diffusers (also called guide wheels) can present serious problems if their thermally induced expansion deviates from that of neighboring parts. This can entail the development of pronounced stresses. The patent to Lindemann et al. proposes to provide the guide wheels with deformable projections which can conform to the shapes of neighboring parts in that the parts (projections) which undergo more pronounced thermally induced expansion are free to slide relative to the neighboring parts. Thus, thermally induced different expansion of neighboring parts is compensated for by deformation of selected portions (projections) of the guide wheels.
The patent to Lindemann further proposes to insert specially designed parts, such as springs, if the expected changes in thermally induced expansion of neighboring parts are quite pronounced. This is intended to ensure that the clearances between neighboring parts are eliminated or are kept within an acceptable range.